A loaded "RG 22" pistol (a cheap cast aluminum revolver that sprayed as much lead out the cylinder to forcing cone gap as went out the barrel) wrapped in a shop rag in a wall with no access.
"#10 Downing Street" (the address of the British Prime Minister) written in 2' high letters inside a wall.
A hollowed out elephant's foot (complete with toenails) in an attic.
Everyone should have one of these ...S